This year’s flu shot will be missing a strain of influenza it’s protected against for more than a decade.

That’s because there have been no confirmed flu cases caused by the Influenza B/Yamagata lineage since spring 2020. And the Food and Drug Administration decided this year that the strain now poses little to no threat to human health.

Scientists have concluded that widespread physical distancing and masking practiced during the early days of COVID-19 appear to have pushed B/Yamagata into oblivion.

This surprised many who study influenza, as it would be the first documented instance of a virus going extinct due to changes in human behavior, said Dr. Rebecca Wurtz, an infectious disease physician and epidemiologist at the University of Minnesota School of Public Health.